With an increase in demand for handheld devices that feature computing, telephony, faxing and networking capabilities, that players in the industry move to supply better handheld devices at competitive prices is inevitable. For example, a Personal Display Assistant (PDA), which is a type of pen-based handheld device that may function as a cellular phone, fax sender and electronic personal organizer, is a common product offered in the marketplace. Some of these PDAs are controlled by operating systems (OS) which have graphics routines to generate and display graphics and text images of varying sizes. These PDAs, however, usually come with small Liquid Crystal Display (LCD) screens. Due to the small display area of these LCD screens, the displayed images will consequently appear very small and, therefore, can be difficult to view.
Since these LCD screens with small display areas have display resolutions of 640.times.240 pixels, each of these pixels will therefore have a viewing dot of small size and pitch. In addition, LCD screens have poorer viewing contrast compared with Cathode Ray Tube (CRT) monitors. Text images appearing on such small LCD screens, especially those with small font sizes, therefore are extremely difficult to read. A simple solution to this reading problem would be to enlarge, or zoom into, a window, or a part, of the text image. Such a solution can be implemented using known software or software-plus-hardware scaling techniques.
Conventional PDAs come with monochrome displays which apply a simple software-based bitmap scaling technique. Such a technique, however, produces unsatisfactory visual effects such as an increase in aliasing, which has the effect of increasing the jagged, or stairsteps-like, appearance of the diagonal edges of graphics or text images. For example, the slanting edges of a black letter "A" on a white background, when stretched vertically and horizontally using the simple conventional software-based bitmap scaling technique, may become more jagged and uneven. Designing better text fonts for use with the conventional PDAs is often the only solution to alleviate the problem of increased aliasing caused by the conventional software-based bitmap scaling technique.
Scaling techniques that involve software control and hardware resources are generally more complicated and thus are not cost-effective implementations. Unless the OS or hardware of the PDA can support such scaling operations, the conventional software-based bitmap scaling technique is usually a preferred option.
With the introduction of more advanced grayscale displays for use with PDAs, the appearance of scaled images on these displays can be improved. The effect of aliasing can also be reduced during the scaling operation by applying smoothing techniques, which generally involve steps to smooth out the jagged slanting edges. The generation of a smoothed scaled image, however, can be a computationally expensive task and, therefore, time consuming. Since near real-time performance is often desired of any scaling operation, it is inevitable that a scaling technique which uses minimal computational resources is sought.
The present invention provides a solution to various prior art deficiencies, which include those present with the conventional software-based bitmap scaling technique described in the preceding paragraphs, to provide a cost effective and fast image scaling method.